The terminal nerve (TN) is a ganglionated nerve located in the nasal and rostral intracranial cavities of all vertebrates. The presence of LHRH-like peptide within the TN and the TN's apparent connections with chemosensory and reproductive neural targets (and the retina in some species), suggests that the TN may coordinate the perceptual, neuroendo-crine and behavioral events which lead to a successful copulatory act. We have previously shown that lesions of the TN impair the mating behavior of the male hamster. The mechanism by which these deficits occur is not known. Our anatomical data suggest that the TN interacts extensively with the vomeronasal system in the hamster and may modulate behavior and other physiological events by influencing this latter system. However, in sub-mammalian species the TN appears to have quite different anatomical projections within the nasal cavity and brain. Thus a comparative approach to studying the TN might aid us in formulating a general hypothesis on TN function. The goals of the proposed research are 1) to investigate further the role which the TN might play in reproductive behavior and neuroendocrine responses in both the male and female hamsters, and 2) to examine the anatomy and development of the TN in more detail. With a better understanding of the connections between the TN and other neural structures, such as olfactory epithelium and retina, we can better understand the mechanism by which this nerve may affect the animal's behavior. Experiments to trace the projections of the nerve and to examine its development and ultrastructural characteristics are proposed. In addition, the effects of TN lesions on sexual behavior, on neuroendocrine responses to pheromonal stimulation and on peptide content in neural target tissues will be investigated. Since the TN may represent a direct pathway from the nasal cavity to reproductive areas of the brain, research in this area may further our understanding of how chemosensory information may influence reproduction in normal and abnormal disease states.